Funds have been requested to purchase a newly developed, state-of-the-art analytical ultracentrifuge (the Beckman XL-A). This instrument will replace an existing analytical ultracentrifuge (the Beckman Model E), which is over 30 years old, and has become virtually impossible to maintain. The investigator group consists of six faculty in the Department of Biochemistry at the University of Texas Health Science Center at San Antonio. Each of the six faculty directs PHS-funded research program(s) involving investigations of macromolecular structure and function, and each utilizes analytical ultracentrifugation as a component of their research activities. The requested analytical ultracentrifuge will provide a stable, dependable means to continue these experiments, which include investigations of: 1) chromatin structure and stability, 2) cytochrome oxidase monomer-dimer equilibrium, 3) mechanisms of oxidation and folding of the mitochondrial enzyme rhodanese, 4) bacteriophage structure and conformation, 5) mechanisms of assembly of the multienzyme complex pyruvate dehydrogenase and 6) the interactions between flavoproteins and heme proteins in the microsomal electron transport system mediated by cytochromes P450. In addition to replacing outdated technology, acquisition of a modern analytical ultracentrifuge will allow this group of six investigators with diverse bioanalytical research programs to demonstrate, through research publications, the usefulness and importance of analytical ultracentrifugation as a contemporary research tool. This in turn will help re-educate the scientific community about a powerful technique which has essentially disappeared from today's arsenal of technical approaches.